Hydraulic fracturing is used to fracture rock surrounding a treatment well and pump the created fractures with a mixture of fluid and granular media (proppant) to enhance the permeability of the rock formation adjacent the treatment well. If the formation contains a hydrocarbon reservoir, treatments such as hydraulic fracturing seek to increase the production of the reservoir by creating pathways through which the hydrocarbons can flow to the treatment well. A typical scenario is in gas-bearing shale formations where the inherent permeability of the rock is too low to allow for efficient drainage of the reservoir. Hydraulic fracturing allows for the gas trapped in pore spaces of the shale to be produced, even from long distances from a production well, due to the enhanced permeability of the hydrocarbon-bearing formation that the injected proppant imparts.
In the process of creating and reactivating cracks in the formation, hydraulic fracturing generates small-scale seismic events. This seismic energy generated by these events propagates away from the location of the fracture, which is known as the hypocenter. These seismic events, called microseismic events, typically measure less than Mw0 on the moment magnitude scale. In contrast, earthquakes that are felt by humans and reported on surface typically reach magnitudes of Mw3 or more. Moment magnitude (Mw) is a parameter that involves characterization of the low-frequency spectrum of the seismic or microseismic event.
Many injection processes, including for example hydraulic fracturing and cyclic steaming, are monitored through the use of microseismic monitoring. Hydraulic fracturing and cyclic steaming are capable of generating thousands of micro-earthquakes with magnitudes typically ranging from −Mw4 to −Mw1. The instrumentation and configuration of the microseismic monitoring networks are typically chosen with this magnitude range in mind, and the relatively high frequency signals are recorded with geophones with the bandwidth appropriate for accurate spectral characterization.
A seismic monitoring network that enhances frequency range for monitoring seismic events while maintaining the location accuracy from monitoring proximal to the reservoir is desirable.